In the right triangle shown, $AC = 3$ and $BC = 6$. What is $AB$ ? $A$ $C$ $B$ $3$ $6$ $?$
We know $a^2 + b^2 = c^2$ We want to find $c$ ; let $a = 6$ and $b = 3$ So $c^2 = 6^2 + 3^2 = 45$ Then, $c = \sqrt{45}$ Simplifying the radical gives $c = 3\sqrt{5}.$